Flexible Electrochromic Energy-saving Windows with Fast Switching and Bistability Based on Transparent Solid-state Electrolyte

A transparent solid-state electrolyte (T-SE), consiting of polymethacrylate (PMMA), polyoxypropylene glycol (PPG), and lithium perchlorate (LiClO4), was prepared. Using perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) and 5,5'''-di(methylbenzoate)-2,2':5',2'':5'',2'''-quater(3,4-ethylenedioxythiophene) (4EDOT-2B-COOCH3) as electrochromic active materials, the electrochromic devices (ECDs) (include rigid and flexible ECDs) based on T-SE were then fabricated. The ECDs possesed sandwich structure consiting of indium tin oxide (ITO) glass (or ITO polyethylene terephthalate (PET))/PTCDA (or 4EDOT-2B-COOCH3) film/T-SE/ITO glass (or ITO PET ). The ECDs exhibited fast switching speed and high optical contrast. The doping/dedoping switching time of the flexible ECDs (ITO PET/PTCDA film/T-SE/ITO PET and ITO PET/4EDOT-2B-COOCH3 film/T-SE/ITO PET) were 2.4 s/5.6 s and 5.2 s/2.6 s, respectively; and their optical contrast were 61.0% and 48.6% at 700 nm, respectively. Notably, the flexible ECDs (ITO PET/PTCDA film/T-SE/ITO PET and ITO PET/4EDOT-2B-COOCH3 film/T-SE/ITO PET) also showed suitable bistability (open-circuit memory); they could retain 81.5% and 74.7% of their original optical contrast at 700 nm after removing the drive voltage for 12 hours, respectively. Furthermore, the flexible ECDs also exhibited similar electrochromic properties under bending conditions.